Cloning Success Rates Increase for Horses

Three years after the birth of the first cloned mule and horse, scientists are reporting improvements in the number of viable cloned equine embryos that are carried to term. A Texas A&M University (TAMU) researcher says that five clones of cutting horse champion stallion Smart Little Lena are on the ground and thriving, along with a clone of a second donor horse. Two more clones from a third donor were expected to arrive in May. These births and pregnancies represent a staggering success rate because historically, it has taken many more cloned embryos to produce a live foal.

Katrin Hinrichs, DVM, PhD, professor in the Department of Physiology and Pharmacology in TAMU's College of Veterinary Medicine and Biomedical Science, reported TAMU's first successful cloning ventures in spring 2005. Paris Texas, a clone of European show jumper Quidam de Revel, was born on March 13, 2005. Another clone of an unspecified sport horse was born at TAMU later in the year, but his owners did not wish to identify the animal. It had taken 11 cloned embryos for the 2005 births--six in the Paris Texas project and five in the research that produced the unnamed clone.

The five Smart Little Lena foals were born in February and March 2006 as a result of a research agreement between TAMU and the stud's syndicate manager, Bill Freeman (TAMU does not hold a license or patent to clone commercially). Any foals born as a result of the project would go to the owners.

According to Hinrichs, about 6% of cloned cattle embryos are carried to term. Comparatively, in the Smart Little Lena project, 40% of the transferred cloned horse embryos were successfully gestated. Hinrichs' research team had transferred 13 cloned embryos into recipient mares, and nine pregnancies resulted. Two pregnancies were lost during gestation. Of the seven foals that went to term, one was stillborn and another died the day after it was born. The additional foal of a second genotype (from one established pregnancy) is on the ground and healthy. Additionally, there are two pregnancies (from three initially established) of a third genotype, which were due in May.

In the cloning process, researchers harvest oocytes (eggs) from mares at various points in their reproductive cycles and mature them in an incubator. The scientists then perform nuclear transfers, in which they remove the nucleus from the egg and place a donor cell into the enucleated egg (in this case, a cell from Smart Little Lena). The eggs are then activated, or stimulated to start dividing to form an embryo. Scientists culture the resulting cloned embryos in the laboratory for seven days, and then they are transferred nonsurgically into recipient mares' uteri.

Hinrichs was evaluating oocyte activation treatments in the Smart Little Lena project. She compared injection of a sperm extract with a traditional method--treatment of the egg with a calcium ionophore--and a combination of the two treatments. The combination was the best treatment, although all of the treatments formed blastocysts (the embryo at the stage that it is normally transferred to the uterus) and the differences between them were not statistically significant. She says researchers in horse cloning only get about 0-13% blastocyst formation after activation.

A notable aspect of cloning is that the cells for white pigmentation can migrate differently in different individuals, just as monozygotic calves might have spots in different places. In these cases, the Smart Little Lena clones have slightly different markings.

"The neat thing is Smart Little Lena is a sorrel with a blaze...and the white is there on every foal's face, although the migration (of the color) is somewhat random," said Hinrichs. "There's only a star and a snip in one of the foals. The blazes all tend to go off to the right a bit."

The cloned Smart Little Lena colts are healthy and are growing quickly, and Hinrichs says that Freeman intends to use them as breeding stock since Smart Little Lena is aging. The National Cutting Horse Association doesn't require horses to be in a breed registry (only a European breed registry has agreed to accept cloned horses at this point), so Hinrichs anticipates the Smart Little Lena bloodline will be stretched into the future as the get of the clones go on to compete.

Paris Texas has the same destiny--he has since been shipped home to Europe and will be used as a stud. "The owner stays in touch with me and sends me photos; he is very happy with him," Hinrichs said. "This horse (the donor horse) was one of the top stallions in Europe--he's 25 years old now and is siring foals that are winning on the circuit. They wanted to be sure they could continue to produce foals from that bloodline.

"From what we know, there should be no difference between the foals of Paris Texas and the foals of Quidam de Revel," she said, and the same should hold true with Smart Little Lena's clones.

About the Author

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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